(a) Field of the Invention
The present invention relates to a liquid crystal display and a method of driving the same and, more particularly, to a liquid crystal display which controls a gamma curve to be adapted to the input gray scale data, thereby displaying a high contrast screen image without any loss in the gray scale data.
(b) Description of the Related Art
Generally, in the case of liquid crystal displays, the required number of gray scale voltages is in direct proportion to the number of data bits. For instance, three bits of data correspond to eight gray scale voltages. Recently, it has been proposed that six or eight bits of data might be used for the display application, and hence, the required number of gray scale data should be increased as much.
Meanwhile, it is difficult to make all of such increased number of gray scale voltages in a separate manner. Therefore, the drive IC for the liquid crystal display receives only eight or nine gray scale voltages from the outside while producing the intermediary gray scale voltages in situ by way of resistance division.
For instance, ten gray scale voltages V0 to V9 are input from the outside, and the intermediary voltage values are generated within the drive IC in accordance with a predetermined rule. The sequence of the gray scale voltage values is inclined while forming a curve. As the light transmission of the liquid crystal is made in a nonlinear manner, it should be corrected to obtain a uniform light transmission characteristic. This is called the “gamma correction,” and the curve used for the gamma correction is called the “gamma curve.”
FIGS. 1A to 1C are graphs illustrating such gamma curves where the range of brightness is indicated as a function of the range of gray scale data. As shown in FIG. 1A, the usual TFT LCD module is established to have a gamma curve of γ=2.2.
However, such a rigid gamma curve irrespective of the input gray scale data involves several disadvantages.
In the case of a relatively bright screen image such as a scene of seashore, most of the input gray scale data involve high brightness and hence, contrast becomes to be deteriorated over the entire screen area. That is, as shown in FIG. 1B, the brightness range becomes shorter, resulting in deteriorated contrast.
As shown in FIG. 1C, in the case of a relatively dark screen image such as a scene of forest, most of the input gray scale data involve low brightness and hence, contrast again becomes to be deteriorated over the entire screen area.
For this reason, in most of LCD monitors or graphic cards, it is established that the user himself can directly select and use a suitable gamma curve.
In case the user mainly makes use of a bright screen, the gamma constant is established to be more than 2.2. By contrast, in case the user mainly uses a dark screen, the gamma constant is established to be less than 2.2. In this way, the brightness range becomes to be widened, thereby enhancing the contrast.
However, the above-like technique of controlling the gamma curve involves the following problems.
As the gamma curve is fixedly established or manually controlled, the gamma curve control should be made one by one at the respective display screen states. In the case of γ>2.2, the dark display screen becomes to be darker while deteriorating the contrast. By contrast, in the case of γ<2.2, the bright display screen becomes to be brighter while deteriorating the contrast.
Furthermore, in the case of γ>2.2, the gray scale data is taken away by a predetermined amount so that data loss is made at the color area close to black. By contrast, in the case of γ<2.2, the gray scale data is added up by a predetermined amount so that data loss is made at the color area close to white. This makes it impossible to express all of the desired gray scale data.
For instance, when zero (0) to sixty three (63) gray scale data are displayed, the gray scale data may be shifted through adding up or taking away four (4) gray scale data. In this case, zero to third gray scale data close to full black, or sixtieth to sixty third gray scale data close to full white are lost.
As the gamma curve control is made in larger scale, the amount of data irrelevant to the desired gray scale expression is increased as much.